Research On Walking Method Of Quadruped Robot On Complex Terrain And Environment

About fifty percent of the surface of earth is rough terrain, such as mountainous region, steep slope, marsh and so on. The wheeled or tracked machines are unable to walk through the rough terrain with high degree of roughness. However, many four-legged terrestrial animals can walk flexibly on these types of rough terrains. They have a great advantage in terms of load capacity, complex terrain adaptability, flexibility, and energy efficiency and so forth.The quadruped robots inspired by the quadruped mammals have the stronger loading capacity and better stability than biped mobile robot as well as simpler structure than hexapod robots and eight-legged robots. Therefore, the quadruped robots are the optimal form among the multi-legged robots considering all the factors, like manufacturing cost, controlling complexity and stability and so on, together. Given the advantages of the quadruped robots, research of quadruped robots have glamourous future as platform for application of topographic surveying, adventure project, disaster relief, military reconnaissance, environmental monitoring, and other related areas.The mechanical structure of quadruped robot is complex, and quadruped robot is a non-linear, multibody dynamics system. In order to develop a high performance quadruped robot with highly dynamics, fast speed and more payload capability should break through some key technologies, such as mechanical construction design, kinematic analysis, stability evaluation method, gait planning, foot force control problem, system integration and so on. This dissertation focuses on gait planning methods of quadruped robot based on improving the environmental adaptability and motion stability. By studying the structure and gaits of quadruped robots, a series of control methods are proposed, the content mainly includes the following aspects:1、To ensure all the joints of the quadruped robot accurately follow a given signal is the foundation of the quadruped robot motion control. The kinematics model of the quadruped robot is set up based on the analysis of the topological structure of the quadruped robot. Then, a single joint servo controller the quadruped robot based on speed feedback is proposed. In the single joint servo controller, the desired angular velocity of the joint calculated by the desired trajectory and the Jacobian matrix is used as the feedforward of the servo system, and the performance of the single joint servo controller can be significantly improved.2、In order to ensure the quadruped robot can walk through the rough terrain with lower degree of roughness, a continuous static gait planning method is proposed in this paper. During the process of the quadruped robot’s walking, the torso of the quadruped robot is parallel to the horizontal ground and moves forward with a certain speed. In this way, the average speed of the robot can be improved while the gait planning method is simplified. By increasing the swing movement of the center of gravity (COG) of the quadruped robot in the four leg support phase, the stability of the robot can be improved effectively. In addition, the swing foot trajectory planning method is proposed in this paper. The swing foot can reach the target foothold accurately by using this method.3、Although the average locomotion velocity is lower when the quadruped robot walking forward with the discontinuous gait, the stability margin of the quadruped robot can be effectively increase. In this paper, a discontinuous gait planning method is proposed. The proposed static gait planning method consists of three parts:the posture adjustment planning method, the body trajectory planning method and the foot trajectory planning method. By using the planning methods in the three part, the stability of the robot can be effectively ensured in the walking process, and thus improve the terrain adaptability of the quadruped robot.4、The natural terrain often contains the forbidden areas where feet cannot be placed. In this case, a non-periodic static gait called free gait can be used to ensure the quadruped robot walk through these types of terrain, successfully. In this paper, a continuous free gait planning method is proposed in this paper. Under the assumption that a set of the positions which can be selected as the foothold is given, the quadruped robot can select the swing foot sequence and choose the best foothold for the swing foot automatically. With the aid of a body sway motion, the stability margin of the robot is no less than the minimum stability margin during the whole walking process. With the free gait generation method proposed in this paper, the robot can autonomously navigate through rough terrains as soon as possible on the condition that the robot has enough stability margin.5、In the walking process of the quadruped robot, the application of force control method can improve the compliant of the gait, and then the stability of the robot can be further improved. In this paper, the force control methods for the quadruped robot walking with the static gait/free gait are studied in this paper. This paper detailed analysis the force control method based on dynamic model, the force control method based on the PD controller. The force control method based on foot force distribution and the force control method based on impedance controller are proposed in this paper. Through the application of these methods, the quadruped robot realizes the force control and obtains more excellent performance.